In the production of heavy and viscous hydrocarbon fluids, these fluids often need to be heated up inside the subterranean formation. At a higher temperature, the heavy oil becomes less viscous and can flow easier through the porous channels in the formation.
There are many ways to heat up the fluids. The most common method is to inject water that is at a higher temperature than that of the formation. Often, steam is injected because it has a much higher heat content than hot water. The injected steam cools down and condenses as it contacts the cooler formation rocks and fluids. During this condensation process, energy is transferred to the cooler surroundings. In general, steam can heat up and thin out the heavy oil more quickly than ordinary hot water injection.
There are two types of steaming operation that are currently used in oil fields. In the first type, steam is injected continuously into the formation to push the hydrocarbon fluids toward production wells. Toward the end of this continuous steaming process (which can last many years) hot water is usually injected to scavenge the remaining heated hydrocarbon fluids. Finally, cold water is injected as the push water after hot water injection is deemed not economical anymore.
In the second type of steaming operation, steam is injected into the formation for a certain period and then the injection is stopped. During this "soaking" period, the injected steam presumably condenses and thereby heats up the reservoir fluids. The heated hydrocarbon fluids and the condensate of injected fluid are then produced back from the same well. This process is commonly called cyclic steaming or the "huff-n-puff" process.